In machines for removing and remounting tires from and onto both automobile and heavy vehicle wheels, the shaft which carries the rim self-centering and locking device is generally rotated by an electromechanical geared motor unit. This means that the speed of rotation of the shaft carrying the self-centering device is strictly related to the number of poles in the electric motors being used. Two-pole motors are normally used, and therefore have two fixed speeds of rotation.
In this field there is a need to vary the rotational speed according to the operations carried out and the type of rim and tire being used. Geared electric motors are not able to satisfy these requirements unless special very costly and therefore inconvenient means are used.
The object of the present invention is to satisfy said requirements, this object being attained by using a fluid-driven multi-cylinder operating unit in direct engagement with the shaft carrying the self-centering device, said unit being controlled by a valve which throttles the feed pipe to allow the shaft speed to be varied at will.
This method, besides attaining the stated object also has the advantage of not requiring a mechanical reduction gear and, more importantly still, of providing a constant static torque on the self-centering device. Finally, it is possible to use the same source of pressurised fluid to also feed a rectilinear operating (cylinder-piston) unit for operating the self-centering device. The combination and interaction of said devices enables a mechanical system to be obtained which inter alia is very compact and of small overall size.